Pin down language to get a cosmetic (4,6)
I believe the answer is:
nail polish
'a cosmetic' is the definition.
(I know that nail polish is a type of cosmetic)
'pin down language' is the wordplay.
'pin down' becomes 'nail' (I've seen this in another clue).
'language' becomes 'polish' (Polish is an example).
'nail'+'polish'='NAIL POLISH'
'to get' acts as a link.
(Other definitions for nail polish that I've seen before include "digital application" , "cosmetic" , "digital coverage" .)